DOUBLE TROUBLE: After his no-hitter on June 1, the Mets’ Johan Santana has struggled in both of his starts since. Photo: Paul J. Bereswill

During Johan Santana’s bullpen session the other day, he and Mets pitching coach Dan Warthen made an adjustment.

“They made sure he was back with his delivery where he was when he threw the no-hitter,” manager Terry Collins said yesterday.

Well, that’s a promising revelation because Santana was brilliant in his June 1 no-hitter and has been pretty messy since. Tonight against the Orioles will mark the Mets ace’s third start since making history, and Santana is still searching for his first post-no-hitter quality outing.

Santana followed up his gem by getting blasted by the Yankees in the Subway Series opener on June 8, serving up six runs on four homers in five innings. Because he threw a career-high 134 pitches to accomplish the no-no, Santana was working on six days’ rest against the Yanks. Afterward, Collins blamed himself for Santana’s struggles, saying he caused the lefty to become rusty.

Either way, Santana was only slightly better against the Rays in his next start last week. He allowed four runs in five innings, putting 10 men on base with six hits and four walks.

Thus, Santana has yet to pitch well since his no-hitter, which is exactly what people feared would happen. Well, to be fair, the major fear was Santana would get hurt since he had thrown the 134 pitches and was only recently coming off major shoulder surgery. He has been healthy since, which alleviates one concern, but he hasn’t performed effectively.

Collins, who was extremely vocal about his concerns over letting Santana throw the 134 pitches, said yesterday the team is convinced the 33-year-old lefty is OK. Said the manager, “I think he’s fine.”

Perhaps the issue simply has been mechanical. Collins said Santana had gotten away from what he did in the no-hitter — thus, the adjustment in the bullpen with Warthen. It might also help that tonight will be Santana’s first start at Citi Field since the no-no.

Other than a poor start against the Braves on April 17 when he only lasted 1 ¹/₃ innings and allowed six runs (four earned), this season Santana had been terrific before his last two turns. In fact, the no-hitter marked his second consecutive complete-game shutout and lowered his ERA to a sparkling 2.38 through 11 starts.

The Mets can’t expect Santana to be magnificent every turn, but they badly need him to consistently pitch well in order to sustain contention. Santana and R.A. Dickey are a formidable duo, and especially considering the team’s shaky offense (little power, little speed) and atrocious bullpen, strong Santana performances are pretty mandatory.

Which makes one revelation fortunate — while the Mets have been careful with Santana this year, Collins told The Post yesterday he is not under any innings cap this season.

“We were hoping in spring training that he’d get 28-30 starts,” Collins said.

Thus, Santana — assuming he pitched well — would be in line for something in the neighborhood of 200 innings. As of now, he is on pace for 31 starts and 188 innings. He’s exceeded that inning total in six of the last seven years that he has pitched, so he should be able to handle it assuming his shoulder holds up.

Tonight, Santana will try again for the proper no-hit follow-up since it’s been missing in action for a few weeks. He’ll hope that the third start’s the charm.